朕得一疾 An Illness That Will Not Lift
眾官都在階下跪拜，惟假唐僧挺立階心，口中高叫：「比丘王，請我貧僧何說？」君王笑道：「朕得一疾，纏綿日久不愈。幸國丈賜得一方，藥餌俱已完備，只少一味引子。众官都在阶下跪拜，惟假唐僧挺立阶心，口中高叫：「比丘王，请我贫僧何说？」君王笑道：「朕得一疾，缠绵日久不愈。幸国丈赐得一方，药饵俱已完备，只少一味引子。
逐句解 Line by line
The assembled officers all knelt and bowed at the foot of the steps, but the false Tang Monk stood bolt upright in the middle of them and called out in a loud voice, "King of Bhikṣu, what do you want with this poor monk?"
The staging carries the joke. Everyone else is face-down on the ground; the monk stands. A real Tripitaka would never do this, and the court is too rattled to notice. 貧僧, "this poor monk," is the humble self-reference a monk uses before a ruler — delivered here at a shout, standing up, which drains the humility straight out of it. Bhikṣu (比丘) is the Sanskrit word for a fully ordained monk, so the kingdom is named, with some irony, after the very thing its king is about to butcher.
The king said with a smile, "We have contracted an illness that has dragged on many days without mending.
朕 is the imperial "we," reserved for the emperor alone since the First Emperor claimed it. 纏綿 is a lovely word to find here: it means "entangled, clinging," and is more often used of a love that will not let go. Applied to a fever it gives exactly the sense of an illness that keeps its arms around you.
Happily the Royal Father-in-Law has bestowed on us a prescription. The drugs are all prepared and ready; only one ingredient is wanting, the one that carries the rest.
引子 is a real term from Chinese medicine — the "conducting" ingredient, added to a formula to carry the other drugs to the part of the body that needs them. Ginger and jujube are ordinary examples. So the king is not asking for the medicine; he is asking for the delivery vehicle, which is why the request can be framed as a small favour. 藥餌 pairs the word for drug with the word for bait, and the second character is doing more work here than the king knows.
The king's manner is worth watching. He smiles. He explains. He treats the request as a reasonable administrative matter, and the horror of it is left entirely to the reader to supply. This is the novel's usual method with atrocity: nobody in the room says anything shocking.
The medical vocabulary is accurate, which sharpens the effect. A 引子 really is the last thing added to a prescription, and a court physician really would speak of one being "wanting." The Royal Father-in-Law has built his demand inside a genuine framework, so that it arrives sounding like pharmacy rather than murder.